Optical characterization of carbon ion implantation into Si and SiGe alloys

Abstract

ABSTRACTSi and epitaxial SiGe strained and relaxed layers have been implanted with C ions to investigate the formation ofSicy and SiGeC alloys (medium doses) as well as the ion beam synthesis of SiC in SiGe matrices (high doses). These layershave been analyzed by Raman scattering, in correlation with XRD, XPS and TEM. These data show that for implanttemperature of 500°C (crystalline target), carbon is not incorporated in substitutional sites, and 3-SiC precipitates aligned withthe implanted matrix are formed. The residual strain and the degree of missorientation of these precipitates depend on thestrain, defects and bond length of the implanted matrix. Moreover, precipitation of 3-SiC in the implanted region causes anenhanced Ge migration, mainly towards the surface. This determines a Ge enrichment and consequent relaxation ofthe Si1Gematrix. This contrasts with the room temperature implants performed in preamorphized Si layers, where carbon incorporationin substitutional sites (Cs) takes place after thermal annealing. The maximum amount of C is found for the implanted dosecorresponding to a peak carbon concentration of 1 .3%. For higher doses, there is a degradation of the crystal quality of therecrystallized layer.Keywords: Raman Scattering, Ion Implantation, SiC, SiGeC, Silicon Carbide.1. INTRODUCTIONIn the last years there has been a strong interest in the growth and characterization of group IV semiconductorheterostructures. This has been related to the recent research on new binary and ternary materials, as SiC and SiGeC, aswell as to the strong development achieved in SiC based technologies for electronic devices and sensors.The possibility to incorporate substitutional C in Si and SiGe alloys without loosing the high crystalline quality ofthe layers has opened the opportunity of band-gap and strain engineering in Si based technologies, something which up toknow was restricted mainly to 111-V compounds. The SiGe system has been extensively studied, being its technology matureenough to be used in modern devices as heterojunction bipolar transistors with enhanced performance. In contrast with Ge,which is soluble in Si over the entire composition range, the solid solubility of C is less than 2xl03 at%. In spite of this,metastable Si1C and Si1..GeC layers with carbon content about 1% have been grown by different techniques includingMolecular Beam Epitaxy (MBE), Chemical Vapour Deposition (CVD) techniques and ion implantation'5. In the last case, ionimplantation was followed by Solid Phase Epitaxy (SPE) growth of the layers. In relation to the other techniques, ionimplantation has potential advantages, related to its higher compatibility with Si integrated circuit processing technologies.By these processes, high crystalline quality SiC tensile and SiGeC strain compensated layers have been grown47. Strane eta14 have observed a metastable solubility limit for the incorporation of carbon into Si by ion implantation and SPE to be inthe range 0.7%-i .4%. This solubility limit is likely determined by strain accumulation -related to the strong local distortionaround C atoms- at the amorphous-crystalline interface during SPE growth. On the other hand, SPE has also a problem, relatedto the presence of End-Of-Range (EOR) defects in the amorphous-crystalline interface region. In principle, these problemscould be avoided by performing the implantation at temperatures high enough to inhibit amorphization in the implanted region.